Technical Field
The present invention relates to a process for manufacturing a lid for an electronic device package, to a process for manufacturing a packaged microelectromechanical device, to a lid for an electronic device package, and to a packaged microelectromechanical device.
Description of the Related Art
MEMS (microelectromechanical systems) devices find increasingly extensive use in a wide range of sectors as miniaturized sensors or transducers. For example, microphones and pressure sensors are frequently used in mobile communication devices and filming apparatuses, such as cell phones and video cameras.
Given that the extremely marked miniaturization of MEMS devices entails a certain fragility of micromechanical structures, it is common to use protective lids that encapsulate the parts more readily subject to failure. Normally, MEMS sensors or transducers are mounted on substrates, possibly with control circuits. The substrates are coupled to respective lids and form packages within which the devices to be protected are located.
The protective lids also perform other functions, in addition to that of mere mechanical barrier.
In particular, in many cases, the transmission of the signals may be disturbed by the environment, and hence it is necessary to envisage a protection from light and electromagnetic interference. For this purpose, the cavities of the lids are coated internally by metal shielding layers. The lids may moreover have the function of determining optimal conditions of acoustic pressure for operation of the MEMS sensors.
The protective lids are in general bonded to the substrate on which the MEMS sensors are mounted by conductive glues, which enable grounding of the electromagnetic shielding layer.
Soldering pastes, for example with a base of tin-lead, tin-aluminum-copper, or tin-antimony, would in themselves be preferable to conductive glues, especially on account of the better resistance to impact demonstrated by the results of drop tests. However, soldering pastes melt during the steps of assembly of a package (comprising supporting board, MEMS sensor, and lid) to the boards of the electronic system in which the MEMS sensor is to be used. Molten soldering pastes tend to climb up the vertical conductive walls of the lid, invading the cavities in which the MEMS sensor is housed and leaving empty spaces in the soldering joints. The empty spaces in the soldering joints are particularly undesirable, because, on the one hand, they weaken soldering and, on the other, may cause leakages that affect the performance of the devices, especially when a controlled-pressure reference chamber is desired.
There is thus felt the need to allow the use of soldering pastes in the production of packaged electronic devices comprising microelectromechanical structures.